The present invention relates to a reformer controlling apparatus in a fuel cell power generation system.
As a reformer controlling apparatus in a conventional fuel cell power generation system, there has heretofore been the one disclosed in Japanese Patent Laid-Open No. H11-92102. In this conventional reformer controlling apparatus, a fuel reformer uses the air as oxidation gas, and methanol is made to perform either a steam reforming reaction or a partial oxidation reaction, followed by generation of hydrogen rich reformer gas. Thus, the hydrogen rich reformer gas is supplied as fuel gas for a fuel cell.
A reaction formula expressing steam reforming of methanol is shown below.
CH3OH+H2Oxe2x86x92CO2+3H2xe2x88x9249.5 (KJ/mol)xe2x80x83xe2x80x83(1)
As shown in the Equation (1), since the steam reforming reaction is an endothermic reaction, it is necessary to supply heat energy to progress the reforming reaction. To supply this heat energy, a method is employed, in which the methanol is made to perform the partial oxidation reaction that is an exothermic reaction, and the steam reforming reaction is progressed by using heat generated in the partial oxidation reaction. A reaction formula expressing the partial oxidation reaction of methanol is shown below.
CH3OH+xc2xdO2xe2x86x92CO2+2H2+189.5 (KJ/mol)xe2x80x83xe2x80x83(2)
As shown in the Equation (2), the partial oxidation reaction is an exothermic reaction.
However, the partial oxidation reaction shows a reaction rate faster than that of the steam reforming reaction. For this reason, in a method in which oxidation gas is supplied to a fuel reformer together with methanol and steam, and heat energy produced in the partial oxidation reaction is utilized in the steam reforming reaction, there has been a problem that a temperature distribution is uneven in the interior of the fuel former particularly in a transient state. Specifically, on an upstream portion in the fuel reformer, that is, on a portion where gas containing methanol, steam and oxidation gas is introduced, a temperature in the interior of the fuel reformer rapidly rises to form a peak of the temperature distribution, resulting in unevenness of a temperature distribution state.
To cope with this problem, the conventional reformer apparatus comprises means for determining a quantity of oxygen to be supplied to a fuel reformer based on a driving quantity of a pump for supplying methanol from a methanol tank to an evaporator, which makes methanol and water evaporate, and oxygen concentration regulation means for controlling an oxygen concentration in oxidation gas to be supplied to the fuel reformer. In the conventional reformer controlling apparatus, when a temperature on an upstream portion of the fuel reformer rises to a specified value or more, the oxygen concentration in the oxidation gas is reduced without changing the quantity of oxygen, and, to the contrary, a flow amount of the oxidation gas is increased, whereby a partial oxidation reaction on the upstream portion of the fuel reformer is suppressed. At the same time, a flow rate of the gas in the interior of the fuel reformer is increased, whereby an area where the partial oxidation reaction is chiefly performed is made to be broadened to a down stream portion of the fuel reformer. Thus, a temperature distribution in the fuel reformer is made to be uniform.
Incidentally, in such conventional reformer controlling apparatus, the concentration of oxygen in the oxidation gas is controlled without changing the quantity of oxygen depending on a temperature of the fuel reformer. Accordingly, if an error occurs in feed amounts of methanol and steam supplied to the fuel reformer, the quantity of oxygen supplied to the fuel reformer is either too much or too little, and this causes abnormality in a temperature of the whole of the fuel reformer. There have been problems of stopping the reforming reaction and exhausting unreacted gas from the fuel reformer.
A case where an output is increased is considered. The driving quantity of the pump for supplying the methanol from a methanol tank to an evaporator increases. In accordance with the increase in the driving quantity of the pump, the quantity of oxygen supplied to the fuel reformer also increases. Nevertheless, the supply of methanol to the fuel reformer is delayed for a time when the methanol evaporates in the evaporator. The fuel reformer is operated in an oxygen rich state during the evaporation of the methanol. As a result, a temperature at the upstream portion of the fuel reformer rises. In response to the temperature rise of the fuel reformer, the oxygen concentration is decreased to increase in gas flow rate within the fuel reformer. However, when a quantity of methanol enough to consume the oxygen supplied to the fuel reformer is not supplied, only the partial oxidation reaction is performed in the fuel reformer, and the temperature in the whole of the fuel reformer rises. Thus, the oxygen concentration in the oxygen gas is more decreased, and hence the gas flow rate within the fuel reformer is made to be faster. The unreacted gas such as the methanol, the steam and the surplus oxygen is exhausted from the fuel reformer.
The present invention has been made in consideration of the above-described problems. The object of the present invention is to provide a reformer controlling apparatus capable of controlling a ratio of reactions in the whole of a catalyst unit to those in other units, particularly a ratio of the partial oxidation reaction to other reactions, to a desired value, and capable of performing a stable reforming reaction without producing a local high temperature state in the catalyst unit particularly during a transient state in which an output is changed.
To achieve the above object, a reformer controlling apparatus of the present invention is provided with a reformer having a catalyst unit composed of a catalyst for promoting a steam reforming reaction and a catalyst for promoting a partial oxidation reaction, a raw fuel gas supplier supplying raw fuel gas containing hydrocarbon and steam to the catalyst unit, an oxidation gas supplier for supplying oxidation gas containing oxygen to the catalyst unit, a first reaction state detector detecting a state of a reaction progressing at an upstream portion of flows of the raw fuel gas and the oxidation gas within the catalyst unit, a second reaction state detector detecting a state of a reaction of the whole of the catalyst within the catalyst unit, a first corrector correcting feed amounts of the raw fuel gas and the oxidation gas supplied to the catalyst unit based on the state of the reaction detected by the second reaction state detector, and a second corrector correcting the feed amount of the oxidation gas supplied to the catalyst unit and/or a feed timing thereof based of the state of the reaction detected by the first reaction state detector.
In other words, a reformer controlling apparatus of the present invention is provided with a reformer having a catalyst unit including a catalyst for promoting a steam reforming reaction and a catalyst for promoting a partial oxidation reaction, raw fuel gas supplying means for supplying raw fuel gas containing hydrocarbon and steam to said catalyst unit, oxidation gas supplying means for supplying oxidation gas containing oxygen to said catalyst unit, first reaction state detecting means for detecting a state of a reaction progressing at an upstream portion of flows of said raw fuel gas and said oxidation gas in said catalyst unit, second reaction state detecting means for detecting a state of a reaction in the whole of the catalysts in said catalyst unit, first correcting means for correcting feed amounts of said raw fuel gas and said oxidation gas, which are supplied to said catalyst unit, based on said state of the reaction detected by said second reaction state detecting means, and second correcting means for correcting the feed amount of said oxidation gas, which is supplied to said catalyst unit and/or a feed timing thereof, based on said state of the reaction detected by said first reaction state detecting means.
Beside, a method of controlling a reformer produces promoting a steam reform reaction and a partial oxidation reaction in a catalyst unit of said reformer, supplying raw fuel gas containing hydrocarbon and steam to said catalyst unit by a raw fuel supplier, supplying oxidation gas containing oxygen to said catalyst unit by an oxidation gas supplier, detecting a state of a reaction progressing at an upstream portion of flows of said raw fuel gas and said oxidation gas in said catalyst unit by a first reaction state detector, detecting a state of a reaction in the whole of the catalysts in said catalyst unit by a second reaction state detector, correcting feed amounts of said raw fuel gas and said oxidation gas, which are supplied to said catalyst unit by a first corrector, based on said state of the reaction detected by said second reaction state detector, and correcting the feed amount of said oxidation gas, which is supplied to said catalyst unit and/or a feed timing thereof by a second corrector, based on said state of the reaction detected by said first reaction state detector.